The invention relates to a pumping method and a pump arrangement for the metered pumping of small quantities of liquid under high pressure.
Pumping methods and pump arrangements of this type are disclosed, for example, in WO 93/18296, EP-A-629265 and WO 96/34196. The stored, kinetic energy of the armature device of these pump arrangements which operate in a pulsating manner act directly via the armature, or indirectly via tappet or valve-seat devices, on the fluid medium to be pumped, these devices being surrounded by the fluid medium. In both cases, the kinetic energy is conveyed by solid bodies abruptly and directly onto the liquid to be pumped, which in quite a few applications may lead to an unfavorable expansion of the pressure wave in the liquid to be metered, with the consequence that the metering cannot be carried out with sufficient precision.
It is disclosed in DD patent specification 213 472 to seal off the armature-space device from the delivery space by means of an elastic, movable diaphragm, the diaphragm being reached through by the tappet, which is acted upon by the armature.
DD patent specification 1574 28 describes a pump arrangement of the generic type for the metered spraying of fuel and/or lubricant or alcohol or water, in which the electromagnetic drive is separated from the liquid-conducting space by means of a blocking element in the form of a diaphragm. The armature or pulse-generating element of the electromagnetic drive strikes against the diaphragm and transmits its stored, kinetic energy to the liquid to be sprayed which is located in the liquid-conducting space.
In the two pump arrangements which are described above and have a diaphragm, although the diaphragm ensures that spaces within the pump arrangement are sealed off, it causes considerable, inadvertent losses of kinetic energy, for example as a consequence of friction between the tappet and diaphragm and/or deformation of the diaphragm, during the transfer of the kinetic energy of the armature or tappet to the liquid.
The object of the invention is to provide a pumping method and a pump arrangement which operate in accordance with the energy-storage principle and with which the metering can be optimized without an inadvertent loss of the stored, kinetic energy occurring. A further object is to keep the electromagnetic drive means and the armature and/or tappet free of the liquid to be metered without an inadvertent energy loss occurring during the energy transfer.
This object is achieved by the features of claims 1 and 22. Advantageous developments of the invention are defined in the subclaims dependent on these claims.
According to the invention, a pressure-surge utilizing space (called pressure space below), which contains the liquid to be metered, is separated by a diaphragm from a pressure-surge generating and accumulating space (called pressure-accumulating space below), which contains a pressure-surge transmitting liquid, the stored, kinetic energy being abruptly transmitted first of all to the pressure-surge transmitting liquid in the pressure-accumulating space and a pressure-surge wave being generated which expands in this liquid and is transmitted by this liquid to the diaphragm and by the diaphragm to the liquid in the pressure space.
The speed of expansion and the energy of the surge wave in the pressure-surge transmitting liquid located in the pressure-accumulating space is dependent on the specific properties of said liquid, and so by appropriately selecting this liquid the energy transfer can be influenced in a specific manner. In addition, the selection of the material and the dimensions of the diaphragm enables the energy transfer to the liquid to be metered in the pressure space to be influenced in a specific and more far-reaching manner by, for example, an elastically extensible, compressible and shock-absorbing diaphragm being used or by an incompressible diaphragm which does not reduce the energy or reduces the energy because of its material properties being used.
In each case, the diaphragm separates the pressure-accumulating space from the pressure space in such a manner that the liquid in the pressure space does not come into contact with the electromagnetic drive means, with the result that even corrosive or aggressive liquids can be metered using the method according to the invention and the pump arrangement according to the invention, a liquid which does not act corrosively or aggressively on the drive means with which it comes into contact being used as the pressure-surge transmitting liquid. Provision merely has to be made here for the small number of parts in the pressure space which come into contact with the corrosive or aggressive liquid to be metered to consist in terms of material of an appropriately resistant material.
It is essential for the pressure space, which is partitioned off from the pressure-accumulating space by the diaphragm, to be connected to a feeding device for the liquid to be metered. It is also expedient if the pressure-accumulating space and/or the flood space, which is still located upstream of the pressure-accumulating space, is filled with a liquid and is connected to an equalizing container containing, for example, the same liquid, with the result that during a pumping and return stroke liquid can be sucked out of the equalizing container or pushed into the equalizing container. It is, moreover, expedient to continuously or intermittently recirculate the liquid in the pressure-accumulating space and/or in the flood space, so that relatively cool liquid is circulated, as a result of which the liquid which is to be sprayed and is in the pressure space is also cooled, if appropriate, and cavitation can thus be avoided at least to the greatest possible extent.